Recovery of hydrocarbons from subterranean reservoirs



* M SS REFEZ WQQZi SEARCH KQEQR! P11979912. XR age-$59003 y 5, 1959 R.L. LINDAUER, JR 2,835,003

RECOVERY OF HYDROCARBONS FROM SUBTERRANEAN RESERVOIRS Filed July 19,1957 LIOUEFIED ALCOHOL GAS OR on. INJECTION INJECTION I 3| Z4 28 I77 P26 30 GAS pnonucnou 22 GAS CAP 48 A9 20 -2| 4 ORIGINAL GAS-OIL councrLAYER I2 34 RESERVOIR ORIGINAL WATER-OIL CONTACT WATER 75 g F6. 2. m V

a. m g 50 O I u U] u:

25 FEG. l-

SIZE OF LAYER OIL FORE VOLUME 9'0 E so 1 REsERvmR OILDISPLACED BY ALAYER $UBSTANCE INVENTOR.

ROBERT L. LIN DAUER JR.,

DISPLACEMENT PRESSURE. PSIG- ATTORlE Y.

United States Patent RECOVERY OF HYDROCARBONS FROM SUBTERRANEANRESERVOIRS Robert L. Lindauer, Jr., Bellaire, Tex., assignor, by mesneassignments, to Jersey Production Research Company, Tulsa, Okla, acorporation of Delaware Application July 19, 1957, Serial No. 673,036

14 Claims. (Cl. 166-9) The present invention is directed to a method forrecovering hydrocarbons from subterranean reservoirs. More particularly,the invention is directed to a method of increasing ultimate recovery ofoil from subterranean reservoirs by improving the natural drivemechanism of the reservoirs. In its more specific aspects the inventionis concerned with recovering increased amounts of liquid hydrocarbonsfrom subterranean reservoirs under substantially natural reservoirconditions.

The present invention may be briefly described as a method forrecovering hydrocarbons from a subterranean reservoir containing liquidhydrocarbons. The reservoir contains a fluid other than the liquidhydrocarbons in contact with the liquid hydrocarbons. The feature of theinvention resides in injecting into the reservoir a suflicient amount ofa fluid in contact with the liquid hydrocarbons at a point adjacent thecontact such that a layer is formed which is at least partially misciblewith the liquid hydrocarbons or at least partially miscible with boththe liquid hydrocarbons and fluid originally in contact with the liquidhydrocarbons, the layer being between the liquid hydrocarbons and thefluid in contact with the liquid hydrocarbons. Thereafter, the liquidhydrocarbons are produced in increased amounts under substantiallynatural reservoir conditions. Stating this otherwise, once the layer orlayers are formed, depletion of the liquid hydrocarbons under theinfluence of the natural gas cap drive or the natural water drive willrecover more hydrocarbon liquids than would have been recovered if theselayers had not been formed.

In the practice of the present invention the fluid in contact with theliquid hydrocarbons is either an overlying gas cap or an underlyingwater body, which assists in driv- ;"ing the liquid hydrocarbon to thepoints of production, or

both an overlying gas cap and an underlying water body. The reservoirsare known to those skilled in the art as gas cap drive, water drive, orcombination gas cap and water drive reservoirs.

In accordance with the practice of the present invention, the injectedfluid is injected adjacent one or both of the contacts. The injectionmay be either into the gas cap adjacent the contact, or into the liquidhydrocarbons adjacent the contact with the gas, or into the liquidhydrocarbons adjacent the water contact or intothe water adjacent to thecontact. The injection may be either in the \liquid hydrocarbons or inthe gas adjacent the contact betweeii the gas and the liquidhydrocarbons and into the liquid hydrocarbons or water adjacent thewater contact. Stating this otherwise, injections of fluids may be madeadjacent both contacts.

Whether the fluids are injected into the hydrocarbon liquid or into thefluid originally in contact with the hydrocarbon liquid depends upon thenature of the injection fluid, its interaction with the reservoirfluids, the relative densities of all fluids, as well as other factors.Under normal field conditions, few wells will be available that arecompleted exactly on the contact of the hydrocarbon liquid and otherfluid in the underground reservoir. However, some wells are usually nearthe contact. Injection will ordinarily be made in existing wells nearthe contact, and the injection fluid will be selected to take advantageof the relative densities of all fluids so that the injection fluid willmigrate to form the desired layer.

When the fluids are injected, forces of gravity, due to the diflerencein density of the injection fluid and the fluid being injected into,will cause the injection fluid to migrate in the reservoir. Thedirection of migration will be up if the injection fluid has lessdensity than the fluid being injected into and down if it is more dense.Depending upon the nature of the injection fluid and the fluid receivingthe injection, there may be an interaction between the two fluids. If agas is injected into a hydrocarbon liquid, there will be sorption ofcomponents, one from the other, and gas going into solution with thechanged hydrocarbon liquids, beginning on contact of the fluids; and thecharacter of both fluids will change. By the selection of the propergas, this change will cause the injection fluid and the hydrocarbonliquid to become miscible or more nearly miscible. If the injected gashas a lower density than the hydrocarbon liquid, the injected gas willflow up through the hydrocarbon liquid while the interaction isoccurring, and the hydrocarbon liquid will tend to flow down because ofits greater density and to replace downdip hydrocarbon liquidproduction. By this action, a form of counter-current flow will be setup. The exchange of components between the hydrocarbon liquid and theinjected gas will continue as uncontacted liquid is encountered by themigrating injection gas; however, the quantity of hydrocarbon liquidbetween the injection well and the contact with the original gas cap gaswill ordinarily be small, and there will be more injected gas than caninteract with the oil. The upward migration of the injected gas willcontinue until it contacts a fluid of lesser density, and there it willspread out along this contact forming a layer.

From this description, it should be apparent to those skilled in the artof underground reservoir behavior that layers may be formed by injectionin either the original reservoir liquid hydrocarbons or the fluidoriginally in contact with the reservoir liquids, and the injectionfluid can be either liquid or gas in the reservoir.

An important consideration in determining the most desirable point ofinjection is the difference in density between the injected fluid andthe hydrocarbon liquids as compared to the diflerence between theinjected fluids and the reservoir fluid contacting the hydrocarbonliquids. In general, the layer will form more quickly by injection intothe reservoir fluid which has the greatest density difference to theinjected fluid.

The injected fluid may be selected from a large number of fluids whichare satisfactory in the present invention.

The injected fluid may be heavier than the original reservoir fluid incontact with the liquid hydrocarbons or lighter than the originalreservoir fluid in contact with the hydrocarbons. The injected fluid mayalso be lighter than the liquid hydrocarbons but heavier than the gascap gas, or the injected fluid may be heavier than the liquidhydrocarbons but lighter than the underlying water. The injected fluidmay be lighter than the liquid hydrocarbons but richer in ethane andheavier hydrocarbons than the gas cap gas when the fluid in contact withthe liquid hydrocarbons is gas. The injection fluids may be hydrocarbonsor other substances such as CO or certain alcohols.

The amount of the injected fluid may range from about 1 to 50 percent ofthe pore volume of the reservoir occupied by the hydrocarbon liquid.Ordinarily, an amount of about 30 percent of the pore volume of thereservoir may be sufficient to take full benefit of the process,although less injection may still improve reassajoos covery. Experimentsusing a sand-packed tube saturated with the hydrocarbon liquid and thecontact fluid to simulate reservoir behavior are helpful in determiningthe optimum injection volume for the layer. Experimental recoveries byinjecting different amounts of layer substance permit construction of acurve such as Figure 1. Other factors must be considered when applyingthese experiments to the field because the reservoir cannot beduplicated by the sand-packed tube, but such experiments form anexcellent basis for departure. Ordinarily, heavy viscous oils willrequire more injection, and usually a greater volume of fluid will beneeded if the injection fluid is gas than if it is liquid at reservoirconditions.

The injected fluid may be injected into the reservoir over a period oftime from about 1 month or less to several years, depending upon theamount of injection fluid required. For best results the period shouldbe as short as practical while preventing a temporary build-up inreservoir pressure causing reservoir oil migration into the spaceoccupied by a fluid originally in contact with the oil. Ordinarily earlycompletion of injection takes maximum advantage of gravity to place thelayer. A time from about 2 weeks to about 2 years may be required.

The injected fluid may suitably be injected in increments to achievemiscibility or partial miscibility, and the increments of the injectedfluid may be different one from the other, such as, for example, oneincrement may be gas and another increment may be a light oil, or oneincrement may be liquefied petroleum gases and another increment may bea heavier oil or a lighter gas.

The injected fluid, as stated before, may be selected from a largenumber of suitable fluids for injection. As examples given by way ofillustration and not by way of limitation, one type of injected fluid,which forms a layer miscible or partially miscible at least with theliquid hydrocarbons, is a hydrocarbon gas which is richer or has agreater proportion of ethane and heavier intermediate hydrocarbons thanthe gas in equilibrium with the oil. In general, the greater theproportion of ethane and heavier intermediate hydrocarbons, the greaterwill be the solubility of the injected fluid in the oil and the greaterwill be the chances for complete miscible displacement.

Another type of fluid suitable for injection to form a layer at leastmiscible or partially miscible with liquid hydrocarbons may be theso-called liquefied petroleum gas containing propane, butane, pentane,and higher members of the same homologous series up to decane andhigher. Ethane may also form a constituent of the injected mama moderatequantities of methane can be present. The injected fluid may suitably bemixtures of hydrocarbons, such as petroleum fractions, as exemplified bygasoline, kerosene, gas oils, diesel'oils, and the like. Suitably suchliquid petroleu'fiffiab tions may contain dissolved gases. Othercompounds may be used such as carbon dioxide, and the like.

Other types of injection fluids for injecting adjacent the water-oilcontact may be oxygenated compounds, such as the aliphatic alcohols, asexemplified by propyl, butyl, pentyl, hexyl, and the like, alcohols.Other oxygenated compounds, such as acetone and the ketones, maysuitably be used. In a general sense, the compounds suitable for use inthe practice of the present invention may have both oil and watersolubility or preferential solubility for the oil. However, it ispreferred to use hydrocarbon components as the injected fluid since theyare more readily available from an economical standpoint and do not actas contaminants for the hydrocarbons produced during the final stages.

The present invention will be further illustrated by reference to thedrawing in which:

Fig. 1 is a graph illustrating recoveries possible in the practice ofthe present invention;

Fig. 2 is a view in cross section of a subterranean earth formationpenetrated by a plurality of wells for treatment in accordance with theinvention; and

Fig. 3 is a plot of data illustrating oil recovery in accordance withthe invention as a function of displacement pressure.

Referring now to the drawing, numeral 11 designates a subterraneanreservoir which has an original gas and oil contact 12 between theliquid hydrocarbons or oil 13 and the gas cap 14. The reservoir 11 alsohas an original water-oil contact 15 between the oil 13 and the water16. Drilled from the earths surface 17 and penetrating the reservoir 11is a plurality of wells 18, 19, 20, 21, 22, and 23. Referring to thewells 18 to 23, inclusive, well 18 is at least a temporary injectionwell, while wells 19 and 20 are oil-productive wells, and wells 21 and22 are at least temporary injection wells, while well 23 may be agas-productive well.

In accordance with the present invention, the fluid forming a layer atleast partially miscible with the liquid hydrocarbons may be injectedadjacent the original gas oil contact 12. This may be done by injectinga suitable gas through the injection well 21 by introducing a gas havingthe desirable composition and density through line 24 connecting tocompressor 25 and thence by line 26 into well 21. The injected gas is ofsuflicient characteristics that it will migrate through the reservoir 11to form a layer 27 between the liquid hydrocarbons 13 and the gashydrocarbons 14 in the reservoir. Another way is to inject a light oilwith low viscosity such as gasoline, kerosene, gas oil or diesel oilrange into well 21 in a similar manner. Likewise, if desirable, theinjected fluid may be injected through well 22 by injecting a liquefiedpetroleum gas by way of line 28 connecting into pump 29 and to well 22by line 30. By virtue of the characteristics of the liquefied petroleumgas into well 22, the injected fluid migrates through the reservoir 11also to form a layer 27. When fiuid is injected into well 22, it isdesirable that it achieve miscibility with the gas cap gas 14 as well asthe hydrocarbon liquids, otherwise part of the injected fluid will notmigrate to the layer 27 but will remain in the gas cap region asresidual unrecovered saturation. Extra injection to form the desiredlayer size will therefore be required. In some instances it may bedesirable to inject light oil through well 21 and to inject liquefiedpetroleum gas through well 22. This may be done incrementally throughboth wells, may be injected incrementally through well 21 orincrementally through well 22.

When it is desired to inject a fluid adjacent the wateroil contact, asuitable alcohol, for example, may be injected by way of line 31connecting to pump 32 and thence by line 33 into well 18 to form thelayer 34 between the water 16 and the hydrocarbon or oil 13, as shown inthe drawing. The characteristics of the injected fluid introducedthrough well 18 are such that the fluid migrates to form the layer 34.As stated before, under some conditions, it will be desirable to formboth the layer 27 and the layer 34 to provide increased recovery of theliquid hydrocarbons in the reservoir 11.

It is to be emphasized that in the practice of the present invention thereservoir conditions are substantially unchanged. In other words, theinvention here recovers oil through the natural mechanism of recoveringoil from a subterranean reservoir wherein the natural gas cap drive and/or the natural water drive is supplemented and aided by providing alayer at the contacts, with the layer substantially or at leastpartially miscible with the oil in the case of the oil at the gas-oilcontact or miscible with the oil where the layer is at the water-oilcontact. In other words, in the practice of the present invention, it isunnecessary to increase or maintain the natural pressure of thereservoir. Furthermore, in the practice of the present invention it isunnecessary to inject continuously the injected fluid to producehydrocarbons. The hydrocarbons may be produced simultaneously with theinjection of fluid, but the injection of fluid may be terminated andhydrocarbon fluids produced continuously. In short,

it is contemplated in the practice of the present invention thatsimultaneously with the injection of fluids, hydrocarbons may beproduced from the reservoir with the natural drive being supplementedand/or augmented by the presence of the layer miscible at least with theliquid hydrocarbons. Also, it is contemplated in the practice of thepresent invention that after a suflicient amount of the injected fluidhas been injected into the reservoir, the injection of fluid will bediscontinued or terminated and production of hydrocarbons will proceedto allow the improved and increased recovery of hydrocarbons.

As a measure of the recovery possible in accordance with the presentinvention where the natural drive is improved, recoveries from about 80to 100 percent of the communicable pore space in the reservoir may bepossible in the practice of the present invention, whereas under thenatural drive without a layer at least partially miscible with theliquid hydrocarbons, recoveries of approximately 45 percent by gas capdrive may be expected and about 70 percent by Water drive may bepossible.

To illustrate the improved recoveries that may be obtained by thisinvention, an example is submitted for an oil reservoir such asillustrated in Figure 2, where the gas cap was originally the same sizeat the oil zone and where there is a water-oil contact but no pressuresupport or drive from the water. Table I lists data on the reservoir andoil characteristics:

Table 1 Original reservoir pressure 3,200 p.s.i. Original reservoirtemperature 197 F. Viscosity of oil in reservoir .28 cp. Gas originallydissolved in the oil 700 cubic feet per barrel. Stock-tank gravity ofoil 39 API. Barrels of stock-tank oil per barrel of reservoir oil .73.

Natural recovery from this type of reservoir is somewhat dependent uponthe particular relative permeability characteristics of the formationrock and rate of depletion. However, under normal circumstances,recovery by the natural forces seldom exceeds 45 percent of the originalreservoir oil in place. By the injection of a layer substance such aslisted in Table II, the oil recovery may be increased substantially.

By displacing the reservoir oil from a sand-packed tube with the layersubstance at diflerent pressures, a graph such as Figure 3 may beconstructed. With this graph and a prediction of reservoir pressurebehavior, recovery from the reservoir may be closely approximated. Inthe example, using a 90 percent effective sweep factor to conform to theinhomogeneity of the underground reservoir and a decline in pressure toabout 1,560 at final depletion if 0.3 oil pore volume of layer substanceis injected, the recovery may be 83 percent or on the order of a twofoldincrease over that expected if no layer substance is injected.

While the actual mechanism by way of the improved result obtainableherein is not completely understood, it is postulated by way ofillustration and not by way of limitation that the injected fluid musthave the property of forming a layer at least partially miscible withthe oil. It may be desirable for the injected fluid to be miscible withboth the oil and the gas cap gas or water. In this case a smaller volumeof injection fluid is required to achieve high oil recovery and a highpercentage of the injection fluid can be recovered at the end of oilproduction. When the oil is produced and the normal gas cap expansion orwater drive takes place, the miscible layer may be pushed through theoil zone yielding the unexpected oil recovery. When the injectedsubstance is a hydrocarbon gas to form a layer at the contact of thereservoir liquid and the gas cap which is richer or has a greaterproportion of ethane and heavier intermediate hydrocarbons than the gasin equilibrium with the oil, it is postulated that this injected gas,when contacted with the reservoir components, may be dissolved in theoil causing a reduction in viscosity and surface tension and the volumeof the liquid hydrocarbons. The mechanism may also involve sorptionbetween the oil and injected gas and the gas cap gas and the richerinjected gas, which further alters the layer between the gas and oil tomake it miscible with the oil on the bottom side and with the gas capgas on the top side. If the injected fluid is sufficiently rich in theethane and heavier hydrocarbons, complete miscibility may be achievedand oil recovery may approach percent of the communicable pore space. Ina word, any injected gas may be employed which is richer than theequilibrium gas and which will achieve the postulated mechanism to atleast an improved degree.

The nature and objects of the present invention having been completelydescribed and illustrated, what I wish to claim as new and useful andsecure by Letters Patent is:

l. A method for recovering hydrocarbons from a subterranean earthreservoir containing liquid hydrocarbons, said reservoir containing afluid other than the liquid hydrocarbons in contact with the liquidhydrocarbons, which comprises injecting into said reservoir a suflicientamount of a fluid different from the liquid hydrocarbons and the fluidin contact therewith at a point adjacent said contact to form a layer atleast partially miscible with the liquid hydrocarbons between the liquidhydrocarbons and the fluid in contact with the liquid hydrocarbons, saidfluid different from the liquid hydrocarbons being injected into the gascap when the fluid other than the liquid hydrocarbons is gas and intothe liquid hydrocarbons when the fluid other than the liquidhydrocarbons is water, and producing said liquid hydrocarbons from saidreservoir at a point removed from the point of contact undersubstantially reservoir conditions and under the natural drive of thereservoir whereby increased recovery of said liquid bydrocarbons isobtained.

2. A method in accordance with claim 1 in which the fluid in contactwith the liquid hydrocarbons is gas and the injected fluid is lighterthan the liquid hydrocarbons but heavier than the gas and is injectedinto the gas.

3. A method in accordance with claim 1 in which the fluid in contactwtih the liquid hydrocarbons is water and the injected fluid is heavierthan the liquid hydrocarbons and is injected into the liquidhydrocarbons.

4. A method in accordance with claim 1 in which the fluid in contactwtih the liquid hydrocarbons is gas and the injected fluid is lighterthan the liquid hydrocarbons but richer in ethane and heavierhydrocarbons than the gas.

5. A method for recovering hydrocarbons from a subterranean earthreservoir containing liquid hydrocarbons, said reservoir having anoverlying gas cap in contact with the liquid hydrocarbons, whichcomprises injecting into the gas cap of said reservoir a sufficientamount of a fluid having a composition different from the liquidhydrocarbons and the gas in contact therewith at a point adjacent saidcontact to form a layer at least partially miscible with the liquidhydrocarbons between the liquid hydrocarbons and the gas in contact withthe liquid hydrocarbons, and producing said liquid hydrocarbons fromsaid reservoir at a point remote from the point of contact undersubstantially reservoir conditions and under the natural gas drive ofthe reservoir whereby increased recovery of said liquid hydrocarbons isobtained.

6. A method for recovering hydrocarbons from a subterranean earthreservoir containing liquid hydrocarbons, said reservoir having anunderlying water body, which assists in driving the hydrocarbon liquidsto the points of production, in contact with the liquid hydrocarbons,which comprises injecting into the liquid bydrocarbons in said reservoira suflicient amount of a fluid different from the liquid hydrocarbonsand the water in contact therewith at a point adjacent said contact toform a layer at least partially miscible with the liquid hydrocarbonsbetween the liquid hydrocarbons and the water in contact with the liquidhydrocarbons, and producing said liquid hydrocarbons from said reservoirat a point remote from the point of contact under substantiallyreservoir conditions and under the natural water drive of the reservoirwhereby increased recovery of said liquid hydrocarbons is obtained.

7. A method for recovering hydrocarbons from a subterranean earthreservoir containing liquid hydrocarbons, said reservoir having anoverlying gas cap and underlying water body in contact with the liquidhydrocarbons, which comprises injecting into said reservoir a suflicientamount of a fluid diflerent from the liquid hydrocarbons and the gas andwater in contact therewith at a point adjacent at least one of saidcontacts to form a layer at least partially miscible with the liquidhydrocarbons beween the liquid hydrocarbons and said one of the contactswith the liquid hydrocarbons, said diflerent fluid being injected intothe reservoir at a level other than in the water body, and producingsaid liquid hydrocarbons from said reservoir at a point remote from thepoints of contact under substantially reservoir conditions and under thenatural drive of the reservoir whereby increased recovery of said liquidbydrocarbons is obtained.

8. A method for recovering hydrocarbons from a subterranean earthreservoir containing liquid hydrocarbons, said reservoir having anoverlying gas cap and an underlying water body each in contact with theliquid hydrocarbons, which comprises injecting into said reservoir asuflicient amount of fluids having compositions diflerent from eachother and from the liquid hydrocarbons and the gas and water in contacttherewith at a point adjacent each of said contacts to form'a combinedlayer at least partially miscible with the liquid hydrocarbons betweenthe liquid hydrocarbons and the gas and water in contact with the liquidhydrocarbons, said fluids having compositions diiferent from each otherand the liquid hydrocarbons being separately injected into the gas capand into the liquid hydrocarbons, and producing said liquid hydrocarbonsfrom said reservoir at a point remote from the points of contact undersubstantially reservoir conditions and under the natural drive of thereservoir whereby increased recovery of said liquid hydrocarbons isobtained.

9. A method for recovering hydrocarbons from a subterranean earthreservoir containing liquid hydrocarbons, said reservoir containing afluid other than the liquid hydrocarbons in contact with the liquidhydrocarbons, which comprises injecting into said reservoir a suflicientamount in the range from about 1 to about 50 and ordinarily less than 30percent of the hydrocarbon liquid pore volume of the reservoir of afluid ditferent from the liquid hydrocarbons and the fluid in contacttherewith at a point adjacent said contact for a sufficient period oftime to form a layer at least partially miscible with the liquidhydrocarbons between the liquid hydrocarbons and the fluid in contactwith the liquid hydrocarbons, said diflerent fluid being injected intothe reservoir at a level other than in any water body in contact withthe liquid hydrocarbons, and producing said liquid hydrocarbons fromsaid reservoir at a point remote from the point of contact undersubstantially reservoir conditions and under the natural drive of thereservoir whereby increased recovery of said liquid hydrocarbons isobtained.

10. A method in accordance with claim 9 in which the amount is about 30percent of the pore volume.

11. A method in accordance with claim 9 in which the time is about 1year.

12. A method for recovering hydrocarbons from a subterranean earthreservoir containing liquid hydrocarbons, said reservoir containing afluid other than the liquid hydrocarbons in contact with the liquidhydrocarbons, which comprises injecting into said reservoir a suflicientamount in the range from about 1 to about .50 percent of the oil porevolume of the reservoir of a fluid difierent from the liquidhydrocarbons and the fluid in contact therewith at a point adjacent saidcontact for a period of time from about 2 weeks to about 2 years to forma layer at least partially miscible with the liquid hydrocarbons betweenthe liquid hydrocarbons and the fluid originally in contact with theliquid hydrocarbons, said different fluid being injected into thereservoir at a [level other than in any water body in contact with theliquid hydrocarbons, discontinuing the injection of said fluid, and thenproducing said liquid hydrocarbons from said reservoir at a point remotefrom the point of contact under substantially reservoir conditions andunder the natural drive of the reservoir whereby increased recovery ofsaid liquid hydrocarbons is obtained.

13.'A method for recovering hydrocarbons from a subterranean earthreservoir containing liquid hydrocarbons, said reservoir containing afluid other than the liquid hydrocarbons in contact with the liquidhydrocarbons, which comprises injecting in increments into saidreservoir a sufficient amount of a fluid diflerent from the liquidhydrocarbons and the fluid in contact therewith at least at a pointadjacent said contact to form a layer at least partially miscible withthe liquid hydrocarbons between the liquid hydrocarbons and the fluid incontact with the liquid hydrocarbons, said diflerent fluid beinginjected into the reservoir at a level other than in any water body incontact with the liquid hydrocarbons, and producing said liquidhydrocarbons from said reservoir at a point remote from the point ofcontact under substantially reservoir conditions and under the naturaldrive of the reservoir whereby increased recovery of said liquidhydrocarbons is obtained.

14. A method in accordance with claim 13 in which the increments of theinjected fluid are different in composition from each other.

References Cited in the file of this patent UNITED STATES PATENTS2,742,089 Morse et al. Apr. 17, 1956

1. A METHOD FOR RECOVERING HYDROCARBONS FROM A SUBTERRANEAN EARTHRESERVOIR CONTAINING LIQUID HYDROCARBONS, SAID RESERVOIR CONTAINING AFLUID OTHER THAN THE LIQUID HYDROCARBONS IN CONTACT WITH THE LIQUIDHYDROCARBONS, WHICH COMPRISES INJECTING INTO SAID RESERVOIR A SUFFICIENTAMOUNT OF A FLUID DIFFERENT FROM THE LIQUID HYDROCARBONS AND THE FLUIDIN CONTACT THEREWITH AT A POINT ADJACENT SAID CONTACT TO FORM A LAYER ATLEAST PARTIALLY MISCIBLE WITH THE LIQUID HYDROCARBONS BETWEEN THE LIQUIDHYDROCARBONS AND THE FLUID IN CONTACT WITH THE LIQUID HYDROCARBONS, SAIDFLUID DIFFERENT FROM THE LIQUID HYDROCARBONS BEING INJECTED INTO THE GASCAP WHEN THE FLUID OTHER THAN THE LIQUID HYDROCARBONS IN GAS AND INTOTHE LIQUID HYDROCARBONS WHEN THE FLUID OTHER THAN THE LIQUIDHYDROCARBONS IS WATER, AND PRODUCING SAID LIQUID HYDROCARBONS FROM SAIDRESERVOIR AT A POINT REMOVED FROM THE POINT OF CONTACT UNDERSUBSTANTIALLY RESERVOIR CONDITIONS AND UNDER THE NATURAL DRIVE OF THERESERVOIR WHEREBY INCREASED RECOVERY OF SAID LIQUID HYDROCARBONS ISOBTAINED.